It is well known that biological cells may be killed in a manner of Pasteurization, in which the time temperature product of a process is sufficient to denature cell proteins necessary for vitality. Other cell killing mechanisms are known which involve physical process, such as shear forces, ultrasonic cavitation, alteration in membrane properties through the insertion of pores, and the like.
A number of methods are known for reducing bacterial activity in liquids. Traditionally, a so-called "Pasteurization" process is employed, which operates by the principles of thermal denaturation of proteins to inactivate bacteria. Thus, the liquid is raised to a particular temperature for a proscribed duration, to effect a statistical reduction in the number of, or even elimination of all viable bacteria. In an effort to reduce a duration of the process, high temperatures may be employed, which raise the temperature of the fluid to, e.g., 150.degree. C. for 2-4 seconds under pressure, followed by a flashing (rapid boiling) to lower the temperature, thus limiting the duration of the treatment Such systems thus require a verv high temperature, and may alter a taste of a potable liquid or food product, such as is the case with milk. Depending on how the heat is applied, precipitation of proteins in the product or other physical changes may occur. In addition, the presence of oxygen during treatment may cause accelerated oxidation.
The heat treatment processes for fluid food products (e.g., milk) are applied for destroying disease-causing microorganisms, as well as inactivating microorganisms which may spoil the food. In many known processes, the bacterial reduction is a preservation technique which extends the shelf life, but sterilization is not achieved. Some of these pasteurization techniques involving heat treatment of food products, for instance, milk, are disclosed in USSR Pat. No. N 463,250 M KI A 23c 3/02 and N 427532 M KI 28 9/00 A 23c 3/02.
The most widely used Pasteurized technique involves subjecting food products to heat treatment as high as 65-75.degree. C. and exposing same to this temperature for a period of time of 30 minutes. This is the so-called long-term heat treatment. The second technique involves subjecting food products to heat treatment at a temperature of 70-75.degree. C. and exposing same to this temperature for a period of time of 2-4 minutes. The third technique involves subject food products to short term heat treatment at a temperature of 95.degree. C. and exposing same to this temperature for 30 seconds. The fourth technique includes ultra high temperature heat treatment. It involves subjecting food products to a temperature of 110-140.degree. C. and exposing same to this temperature for a period of time of 2-3 seconds. These treatment are thus based on a thermostability time-temperature relationship of microorganisms. Thermostable life-time is defined as a life-time of microorganisms at a given temperature. The higher the temperature, the shorter the thermostable period. An effective Pasteurization treatment thus subjects food products to heat treatment at a certain temperature for a period of time which is longer than the thermostable period.
These prior art techniques are generally directed toward the thermal denaturation of essential cell elements, they effectively cook the treated medium, including any biological organisms therewithin. Thus, proteins lose their tertiary structure, cells are killed, and heat labile components are adversely affected. Sediments may also be formed, which may necessitate regular cleaning of the system, especially any higher temperature portions, such as heat exchange surfaces.
Some of these drawbacks can be avoided by using the direct heat treatment, which heats the product by way of direct contact of the product subjected to Pasteurization with the heating medium, for instance, steam, rather than through a heat transferring surface of heat exchange equipment. This method eliminates release of the milk "stone" in the heating zone and lessens its appearance on other surfaces of the equipment. These known methods transfer the product into the Pasteurizer, and inject steam made from potable water to a desired temperature, for a desired period. The product is cooled and excess water from condensed steam eliminated. This technique allows a relatively quick heat treatment of the product, and has been found of particular use in ultra high temperature heat treatments. The technique avoids exposure to temperatures higher than a desired final temperature, and thus may limit sedimentation, which may appear, for example, as milk "stone" in a Pasteurization process. Where direct steam contact is used, it dilutes the medium, for example up to 30% of the product mass, with an ultra-high temperature Pasteurization technique, which subsequently is often removed.
These known methods of Pasteurization strive to maintain laminar flow of milk during the process, and thus do not atomize the milk As a result, these systems fail to raise the temperature of the bulk of the milk at a rapid rate, and rather gradually raise the bulk temperature to the Pasteurization temperature, at which the milk is maintained for the desired period. Of course, a small surface layer may experience rapid temperature rises.
Zhang, et al., "Engineering Aspects of Pulsed Electric Field Pasteurization", Elsevier Publishing Co. (1994) 0260-8774(94)00030-1, pp. 261-281, incorporated herein by reference, relates to Pulsed Electric Field Pasteurization, a non-thermal Pasteurization method. This method (as well as other biological treatment methods) may be combined with other methods, to enhance efficacy of the composite process, while avoiding the limitations of an excess exposure to any one process.
RU 2,052,967 (C1) relates to a rapid temperature rise bactericidal treatment method, similar to the present method, but intended to non-selectively kill organisms. Abrams et al, U.S. Pat. No. 3,041,958 relates to a steam processing temperature control apparatus. Wakeman, U.S. Pat. No. 3,156,176 relates to a steam Pasteurization system. Stewart, U.S. Pat. No. 3,182,975 relates to a steam injection heater, which employs impeller blades to mix steam and milk for rapid heating. Engel U.S. Pat. No. 3,450,022 relates to a steam infuser for high temperature steam treatment of liquids. Nelson, U.S. Pat. No. 3,451,327 relates to a steam injector for a milk sterilizer. This device is intended to bring the milk to a high temperature, and thus allows thermal communication between the steam and milk prior to venting. De Stoutz, U.S. Pat. No. 3,934,042 relates to a system for treating beverages, including milk, beer, wine and fruit juices, for sterilization or Pasteurization. The liquid is held at elevated temperatures for extended periods. Janivtchik, U.S. Pat. No. 4,160,002 relates to steam injectors for Pasteurizing milk using pressurized steam. Wakeman, U.S. Pat. No. 4,161,909 relates to an ultrahigh temperature heating system for heating, e.g., milk. The milk falls in a curtain configuration in a steam chamber. The milk is held at a high temperature after heating. Nahra et al. U.S. Pat. No. 4,591,463, and Nahra et al. Re. 32,695, incorporated herein by reference, relate to a milk ultra Pasteurization apparatus in which sheets of milk fall within a steam filled chamber for ultra high temperature Pasteurization. Bronnert, U.S. Pat. Nos. 4,787,304 and 4,776,268 relate to an infusion heating apparatus for sterilizing liquid food products, having a porous steam dispensing cylinder or diffuser located along a central axis of a treatment vessel Sanchez Rodriguez, U.S. Pat. No. 5,209,157 relates to a diary preparation system which involves an ultrahigh temperature treatment step.
It is also well known to fuse cell membranes through the use of so-called fusion proteins, chemical agents, photonic effects, and possibly by application of heat. Cell fusion has been used to form hybrid cells or hybridomas, to insert cell surface proteins or to alter cell cytoplasmic chemistry.
The Rapid Thermal Cycle Processing (RTCP) Technology is relatively unexplored as a mechanism for treating of cells. It is known, however, that RTCP is capable of killing bacteria at temperatures below those which tend to denature bacteria.
The RTCP process, also known as MilliSecond Pasteurization ("MSP",) involves the heating of fluid droplets with saturated steam, at a high rate of increase, for example, over a thousand degrees per second, to a desired temperature, typically under conditions which do not denature (a chemical process which alters structure) proteins. When appropriately processed, fluids may be sterilized, without otherwise changing macromolecular structures.
RTCP technology has been proposed for the "Pasteurization" of milk, to kill bacteria and spores in the milk.
A microwave Pasteurization and Sterilization process is disclosed in Stanley E. Charm et al. (Charm Sciences, Inc., Malden, Mass.), U.S. Pat. Nos. 4,839,142, 4,975,246, and 5,389,335, expressly incorporated herein by reference. These patents disclose a process which is said to sterilize food products without substantial protein denaturation by rapid heating (25-80000.degree. C. per second) and cooling of the treated product within a short time.